1. Field of the Invention
The present invention relates to a dielectric film and a method of manufacturing a semiconductor device using a dielectric film.
2. Description of the Related Art
A gate insulating film of a MOSFET constituting a semiconductor integrated circuit is being reduced in size and thickness recently, and when an SiO2 film is used as a gate insulating film, a tunnel current is produced if its film thickness is 2 nm or less, which is a value demanded recently, and a gate leak current increases. Hence, in recent years, it has been examined to replace the gate insulating film material with a high dielectric constant material having a higher relative permittivity than that of an SiO2 film. This method enables the reduction in SiO2 equivalent oxide thickness (EOT) even when the actual film thickness of an insulating film is increased. The EOT required by a recent MOSFET having a gate length of 22 nm or less is demanded to be further reduced, and in order to meet this demand, it is necessary to increase the actual film thickness of an insulating film using a high dielectric constant material and reduce the gate leak current. As one of the methods of increasing the relative permittivity higher than that of an SiO2 film, it has been examined to turn an SiO2 film into an Si3N4 film or into an SiON film by turning SiO2 into a plasma nitride, however, the relative permittivity of Si3N4 is about twice that of SiO2, and therefore, it is not possible to reduce the EOT sufficiently. Hence, an Hf based oxide or Hf based nitride is examined as a high dielectric constant material.
As a method of forming a high dielectric constant film, the CVD (Chemical Vapor Deposition) method, the atomic layer adsorption/deposition method, and the sputter method are cited. The CVD method has problems of the controllability of film thickness, the uniformity, and the reproducibility because of an incubation time in the forming process.
As one of measures to solve these problems, a method of forming a high-k dielectric film using the sputtering method excellent in the controllability of film thickness, the uniformity, and the reproducibility has been proposed.
The specification of Japanese Patent No. 4239015 describes a method capable of suppressing the interface defect and reducing the thickness of an oxide film to 0.6 nm by diffusing a high dielectric constant film in the oxide film by heat treatment at 500° C. to 700° C. after forming the high dielectric constant film on a silicon oxide film and of reducing the EOT by increasing the relative permittivity of an insulating film. This method requires a technique to leave a silicon oxide film evenly in a region where the physical film thickness is 1.0 nm or less and it is important to prevent a high dielectric constant film to be formed thereon from diffusing to the interface between SiO2 and silicon by anneal. A method of forming an oxynitride film, which is a silicon oxide film into which a trace of nitrogen, about a few percents of nitrogen, is introduced, by a radical nitriding process is also described. Further, it is also described that the heat resistance can be improved by 50° C. and the hysteresis can be reduced more than when Hf is formed on a silicon oxide film by depositing HfN on the silicon oxide film to a thickness of 0.6 nm to 1.0 nm by the sputtering that has introduced nitrogen and performing heat treatment.
The reduction in EOT and the increase in leak current are in a relationship of tradeoff, and therefore, the leak current cannot be improved by only reducing the EOT. Therefore, an insulating film forming technique excellent in heat resistance without changing the composition or crystallinity even when heat treatment at 800° C. or more is performed and without increasing the EOT or the leak current is required. If fixed charges are present in an insulating film, hysteresis occurs in the C-V curve and the fixed charges are known to reduce the lifetime of an insulating film and degrade the reliability of a semiconductor device, and therefore, an insulating film forming technique to suppress fixed charges is also required.
However, the respective techniques described above have the following problems.
The technique to form HfSiO by depositing Hf on a silicon oxide film and performing vacuum anneal in an oxygen atmosphere as described in the specification of Japanese Patent No. 4239015 has such a problem that when the thickness of a silicon oxide film is reduced to 1.0 nm or less, Hf diffused in the silicon oxide film in the heat treatment step reaches the silicon substrate interface to produce fixed charges and deteriorate the electric characteristics. Further, the temperature at which Hf is diffused in the silicon oxide film described in the specification of Japanese Patent No. 4239015 is as low as 500° C. to 600° C. and there is no description of the heat resistance in the activation step (1,000° C.) in the CMOS manufacturing step.
Furthermore, the method of forming an oxynitride film, which is a silicon oxide film having a trace of nitrogen, a few percents of nitrogen, introduced therein, by the radical nitriding process, as described in the specification of Japanese Patent No. 4239015 has such a problem that when the silicon oxide film having a thickness of 1.0 nm or less is radical-nitrided, nitrogen and silicon reach the silicon oxide film interface to deteriorate the interface characteristics